Recently, with the development of information communication technology, bi-directional communication via a packet communication network is actively being performed. Particularly, IP telephones to perform telephone calls via an IP (Internet Protocol) network such as the Internet, by using VoIP (Voice over Internet Protocol) to transmit and receive voice data packets via a packet communication network are becoming popular.
On the other hand, services such as telephone reservation services in transportation organizations or medical institutions, or telephone banking services in financial organizations that use push signals (also called tone signals or DTMF (Dial Tone Multi Frequency) signals) have recently become known. In providing such services, it is becoming necessary for service providers to monitor and manage service quality.
For example, there is a following technique that is used as a technique for measuring the voice quality of an IP telephone. More specifically, the number of received packets and the number of lost packets are counted during a preset period of time for each RTP (Real-time Transport Protocol) session, and the packet loss ratio is calculated. Incidentally, whether or not packet loss has occurred can be determined from sequence numbers, for example, that are included in the packets.
Incidentally, when using services as described above with the IP telephone, voice packet and DTMF packets (in other words, non-voice packets) are mixed and flow in the same RTP session. Moreover, one push signal is expressed by plural DTMF packets. Therefore, even though a part of the DTMF packets are lost, as long as other part of the DTMF packets arrive at the transmission destination, the push signal can be recognized at the transmission destination.
However, when measuring the voice quality in the technique described above, analysis is not performed such that the voice packets and non-voice packets are separated. In addition, in the conventional art, there is no technique of determining whether or not loss of the push signal has occurred, when packet loss occurs. Therefore, in the conventional art, the delivery status of a push signal cannot be determined accurately.